Fuel Atomisation

[Bernd Felsche]

Greg Hermann tapped away at the keyboard with:
> DCOE's have _such_ good atomization that you can let off the choke
> about 5 to 10 seconds after a seriously cold start.
> 
> Most carbys are not that good, and port injectors are not even close.

What are the droplet sizes? At what airflow rates? From which jets?

> Squirting fuel on the back side of a closed intake valve (as some
> port injectors do) so as to vaporize it (to make up for the lack
> of good atomization) hurts both volumetric AND thermal efficiency.
> 
> The trick here is to have as much of the _vaporization_ (as
> opposed to atomization) take place _after_ the intake valve has
> _closed_ .

Increased vapourization (due to the greater atomization you say
occurs in a carb.) upstream of the inlet valve is going to help how?

> What this does is let the latent heat of the fuel (as well as of
> any injected water, SHHHH!!) act as an internal coolant during the
> compression stroke. Internal cooling during the compression stroke

How many Joules are going to be absorbed in the vapourization
process? Unless you're evaporating water, you won't be removing
significant heat without running very rich mixtures. 

You said something about BSFC?

> reduces the negative work needed during that stroke, reduces the
> peak temp of the cycle and the EGT, reduces the peak pressures
> during the cycle, and reduces heat rejection to the water jackets
> significantly as well.

Reduces the pressure by how much to vapourize a liquid droplet into
a gas?

Removing an extra kW of heat from the coolant in a 200kW engine has
always been a problem, hasn't it?

> Good atomization also leads to more uniform distribution of the
> fuel throughout the charge, leading to better, faster combustion
> (also more power and efficiency here).

And increases the tendency to detonate (knock).

> All of which add up to improvements in power, efficiency, as well as
> mechanical durability (lower pressures and temps do that!) as a direct
> result of better fuel atomization.
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